Capacitive Touch Panel Structures: G+G, G+F, GFF, OGS, On-Cell and In-Cell
A projected capacitive (PCAP) touch panel is a grid of transparent electrodes under a cover lens, and the structure name tells you which layer carries those electrodes. In G+G they sit on a separate sensor glass; in G+F, G1F or GF2 on a single film or on the cover plus a film; in GFF on two PET films; in OGS on the back of the cover glass; in on-cell displays on the LCD’s colour-filter glass; and in in-cell displays inside the LCD cell itself. For a custom industrial or medical product, the practical choice is usually between G+G and a film-based add-on stack, because on-cell and in-cell touch are built into a specific LCD and cannot be added to another one. Our 3.5-inch S35001D, for example, uses a G+G sensor with a 0.70 mm chemically strengthened cover glass and an FT5446-P03 controller.
What the letters mean
The name lists the layers from the top. G is glass and F is film, usually PET coated with ITO, the transparent conductor. The first G is the cover lens the user touches. A number counts electrode layers on one substrate: GF2 is commonly used for a single film with electrodes on both sides, and G1F for one electrode layer on the cover glass and one on a film. The naming is not standardized. Fieldscale, a touch-sensing simulation company, lists GFF, G1G, GG, single-ITO, OGS and GGG among the common 2D stack-ups, and notes that GFF and GG are the most popular. Before you compare quotations, ask each supplier for a cross-section drawing.
Add-on stacks: G+G, G+F and GFF
In an add-on (out-cell) structure, the touch panel is a separate part placed over the LCD, either with an air gap or with optical bonding. That separation is its main advantage: the same touch panel design works with any LCD, and each can be specified, sourced and replaced on its own.
- G+G uses a second sheet of glass as the sensor, laminated under the cover glass. Glass keeps its shape over temperature and gives a stiff, flat stack. The cost is weight and thickness.
- GFF uses two PET films, one for each electrode direction, laminated to each other and to the cover glass with optically clear adhesive (OCA). Elo describes this construction for its PCAP touchscreens, using ITO below about 24 inches and metal-mesh film for larger sizes. GFF is thin and light, and suits large screens.
- G+F (also written GF, G1F or GF2) puts both electrode layers on one film, or one on the cover and one on a film. It has fewer laminations than GFF and is thinner again.
Worked example: how thick is a G+G stack in practice? The S35001D drawing gives an LCM thickness of 3.10 ± 0.20 mm without touch and a body thickness of 4.70 ± 0.50 mm with touch. The touch stack therefore adds about 4.70 − 3.10 = 1.6 mm, of which 0.70 mm is the cover glass; the rest is the sensor glass, adhesive and gap. For the housing, design the pocket to the maximum, 4.70 + 0.50 = 5.20 mm, not the nominal. The same drawing gives the touch panel’s transmittance as at least 85 %, which is the price in light of adding the layers.
OGS: the sensor on the cover glass
OGS, one glass solution, patterns the ITO electrodes directly on the inside of the cover glass, so there is no separate sensor layer. Topway, a display maker, summarizes the result as thinner and cheaper than separate-panel designs, with the best light transmission of the three integrated types it compares. The weakness is the glass itself: the cover is cut after strengthening and patterning, and that cutting lowers yield and can leave edge cracks that weaken it. On a custom product there is a second issue. The cover lens is now also the sensor, so a cracked cover means replacing the whole touch panel, and every hole, edge shape and print layer must suit the sensor process.
On-cell and in-cell: touch built into the LCD
On-cell displays place the electrodes on the LCD itself, between the colour-filter glass and the top polarizer. In-cell displays go further and build them into the cell; on LCDs the touch electrodes come from a segmented common electrode (VCOM). Fieldscale’s comparison is a useful summary:
- both are thinner, lighter and cheaper to make than an add-on panel, and in-cell is the thinnest of all;
- because the electrodes are closer to the display, they pick up more display noise, so the signal-to-noise ratio is lower than add-on, and lowest for in-cell;
- in-cell touch and display driving share the frame time, which leaves less time for touch sensing.
For an OEM product the deciding point is availability. On-cell and in-cell are made by the panel maker as part of the LCD, so they exist only on panels designed that way, typically high-volume consumer formats. A lower signal-to-noise ratio also leaves less margin for thick cover glass, gloves and water; see capacitive touch with gloves, water and thick glass.
Structures compared
| Structure | Electrodes on | Works with | Strengths | Watch for |
|---|---|---|---|---|
| G+G | Separate sensor glass | Any LCD | Stiff, flat, dimensionally stable | Weight and thickness |
| G+F, G1F, GF2 | One film, or cover plus film | Any LCD | Thin, fewer laminations | Naming varies; check the cross-section |
| GFF | Two PET films | Any LCD | Thin and light; common on large screens | More adhesive layers and lamination steps |
| OGS | Inside of the cover glass | Any LCD | Fewest layers, high transmission | Cover edge strength; cover and sensor are one part |
| On-cell | Colour-filter glass, under the top polarizer | Only the LCD it was built into | Thinner, higher transmittance than add-on | Display noise; panel availability |
| In-cell | Inside the cell (segmented VCOM) | Only the LCD it was built into | Thinnest and lightest | Lowest signal-to-noise ratio; shared frame time |
Choosing a structure for an OEM product
Most industrial TFTs are bought without touch, so the touch panel is an add-on, and the choice is made with the cover lens and the joining method:
- Size and weight. On small and mid-size panels, G+G and film stacks both work; on large panels, film stacks save weight.
- Cover lens. Thickness, shape, holes and printing affect sensitivity and the sensor choice; see touch panels and cover lenses.
- Air gap or bonding. Each glass-to-air surface reflects about 4 % of the light at normal incidence: for glass with a refractive index near 1.5, ((1.5 − 1) ÷ (1.5 + 1))² = 0.04. An air gap between touch panel and LCD adds two such surfaces, close to 8 % of ambient light reflected back at the viewer. Optical bonding fills the gap with material of similar index and removes most of that; see optical bonding vs air gap.
- Controller and interface. The touch controller reports over its own interface, usually I²C with an interrupt line. Our standalone touch-panel references show typical pairings: S700GG-42, a 7-inch panel with a GT911 controller; S700GF2-05, also 7-inch at 164.4 × 99.5 mm; and S10GF2-94, a 10-inch panel with an FT5426G controller at 247 × 152 mm. The display is paired with each panel per project.
- ESD. The cover is the first thing a charged finger reaches; give the discharge a path to ground that bypasses the sensor tail. See the LCD ESD protection guide.
What to send for a touch panel review
| Item | Why it matters |
|---|---|
| Display model, or its active area and outline | Sets the sensor area and the stack under the cover |
| Cover lens drawing: thickness, shape, holes, printing | Drives sensitivity and the choice of structure |
| Gloves, water, cleaning agents, stylus | Defines controller tuning and the sensor pattern |
| Air gap or optical bonding | Readability, stiffness and reworkability |
| Host interface and preferred controller | Driver support and firmware settings |
| Housing stack-up and allowed thickness | Fit with tolerance, not just nominal |
| Operating temperature and ESD level | Materials, grounding and validation tests |
Video: Capacitive Touch Panel Structures Explained
This SuccessLCD explainer shows where the touch electrodes sit in G+G, GFF, G+F, OGS, on-cell and in-cell structures, works through the thickness of a G+G stack, and explains how to choose a structure for an OEM product.
Capacitive touch structure FAQs
What is the difference between G+G and GFF touch panels?
Both put the touch electrodes under a cover glass. G+G uses a second sheet of glass as the sensor; GFF uses two thin PET films with transparent electrodes, laminated with optically clear adhesive. G+G is stiffer and heavier; GFF is thinner and lighter, and common on larger screens.
What is an OGS touch screen?
OGS means one glass solution: the touch electrodes are made directly on the inside of the cover glass, so there is no separate sensor layer. It is thin and transmits light well, but the cover glass becomes part of the sensor, and cutting strengthened glass after patterning can weaken its edges.
What is the difference between on-cell and in-cell touch?
On-cell places the touch electrodes on the LCD’s colour-filter glass, under the top polarizer. In-cell builds them into the LCD cell itself, using a segmented common electrode. In-cell is the thinnest, but it has the lowest signal-to-noise ratio and shares the frame time with display driving.
Can I add in-cell touch to an existing LCD?
No. On-cell and in-cell touch are made by the panel maker as part of the LCD, so they come only with panels designed that way. To add touch to a display that has none, use an add-on panel such as G+G or a film stack, with an air gap or optical bonding.
Adding touch to a display? Send the display model or outline, the cover lens drawing, the conditions of use (gloves, water, cleaning) and the thickness you can allow. We will propose a touch structure and controller. See custom touch panels and cover lenses, or ask about a capacitive touch panel. For a TFT with integrated touch, see custom TFT display options.